Did You Dump Out the Water? When to Answer “No” to Eliminating a Mosquito Breeding Site When Using the GO Mosquito Habitat Mapper.

Our team has received several questions about what to do when mosquitoes are found in a natural habitat, such as an estuary or a wetland.  When you use the Mosquito Habitat Mapper and your mosquito observations are finally logged, you are then prompted to do Step 4, “Eliminating Mosquito Breeding Habitat. By dumping or treating water you can significantly decrease the spread of mosquitoes.”

It’s important to clarify that Step 4 is referring to artificial or natural containers and human created water impoundments. Examples of water impoundments include things such as stock and cattle watering holes (an important source of mosquitoes in areas in the U.S. west), irrigation ditches (a primary source of the mosquitoes that transmit West Nile virus in Colorado, USA), and artificial ponds and water sources that are landscaping features on public and private lands.  These sites collect water for an established purpose and we aren’t suggesting that you remediate these sites. When you are recording these mosquito habitat sites, the right answer is to just say “no”.

In localities where there is a mosquito control agency, they are usually well aware of impoundments and they are often subject to integrated mosquito control techniques, such as the application of mosquito dunkers. However, there are times when you may want to contact the owner of the impoundment. One example is from a student we spoke to in Arizona, who noted that a cattle watering tank was near her home and a source of a troublesome mosquito problem. Since she knew the owner, we suggested that she let him know that the tank was serving as a human health hazard in their neighborhood and that there are inexpensive, non-toxic water treatments (such as Bti-discussed in the last blog) that could be applied in to the tank.

When you encounter water sources on private property, and you know the owner, it is appropriate to educate them about mosquito source reduction. If you don’t know the owner, or the impoundment is on public property and you have identified a mosquito source, the appropriate thing to do is notify your mosquito control or local public health office about your concerns. If you have a water feature on your property, there are methods you can use to remedy the mosquito problem without dumping out the water or harming other organisms/ Some of these are included in last week’s blog.

Our team has also had several questions about what to do when mosquitoes are found in a natural habitat, such an estuary, swamp or natural pond. In such cases it is never appropriate to mitigate the site (and we will update the app to clarify this).  Most people equate wetlands with mosquitoes and there is quite a bit of public pressure in some communities to remove wetlands because they are seen as places for mosquitoes to breed. However, natural wetlands are a very important case where the best answer is to “just say no.” What most people do not know is that natural wetlands may actually be offering mosquito control and protection.

Mosquitoes, along with other aquatic invertebrates living in a wetland, are part of an integrated ecosystem. Mosquito larvae serve as a protein-packed energy packets for other invertebrates as well as amphibians, fish and other wetland species. Wetland wildlife species of birds, bats spiders and others feast on the adult flying mosquitoes. There are several studies that show that mosquito populations are actually reduced when there is a wetland, because they are feeding and maintaining a healthy predator population.  

Worldwide, wetlands are disappearing three times faster than forests (Larson 2018). Until a couple of decades ago, wetlands were viewed as economic property that could be reclaimed for other uses, such as agriculture. There were even federal incentives in the U.S. to drain and fill natural wetlands so that they could be of use to society. But by the mid 1970’s, studies showed wetland loss was resulting in  precipitous declines in fish and water bird populations. Further study has demonstrated the importance of wetlands not only to biodiversity and fisheries but also to other parts of the Earth system. Shoreline stabilization, flood control, ground water recharge, and water quality improvement are some of the critical functions of a healthy wetland.  Wetlands are also of recreational, educational and scientific importance.


Citizen scientists paddling through the bald cypress blackwater swamp, Robertson Millpond Reserve, Wendell, N.C. March 2019 (Image: Author).

As a wetland ages, the nutrients and biomass in the system increases. Most people don’t realize that established wetlands are among the most productive natural ecosystems- rivaling even tropical rain forests. A healthy wetland is more productive than even our most productive cropland.

There is another reason to protect wetlands: damaged and degraded wetlands, such as those that have been either drained or filled, can become “ideal” habitats for some of our disease-vector species. By altering these landscapes, opportunities for standing pools of stagnant water are created. These habitats foster growth of mosquitoes of stagnant water loving species, and because the ecosystem is damaged, the predators have left. Runoff from agriculture, lawns and golf courses can pool in these areas, and the excess nutrients cause algal blooms.  These blooms can support enormous populations of mosquito larvae- another compelling reason to leave wetlands intact.

A close examination of wetlands is a great classroom exercise to demonstrate that in the Earth system, “everything is connected to everything else.” For more information about wetlands, here are some excellent resources to get you started:

What the world needs now to fight climate change:  more swamps. Moomaw, W., Davies, G., and Finlayson, M.  (2018)

Wetlands disappearing three times faster than forests: study. Larson, N. (2018).

Restoration of Aquatic Ecosystems: Science, Technology, and Public Policy. Chapter 6, Wetlands National Academy of Sciences (1992)

Wetlands, Mosquitoes and West Nile Virus. USDA-NCRAS (2008)

We want to thank you for your questions. Every question such as this one helps us to make the GLOBE Observer app better in subsequent versions. We will clarify the instructions for Step 4- “Eliminate mosquito breeding habitat,” in the next version, so that everyone who uses the app is made aware that wetlands actually reduce the numbers of mosquitoes! Contact:


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